ceremonies in new york, virginia and pennsylvania pay tribute to the 2752 victims killed when terrorists hijacked four commercial planes and attacked the u.s. in lower manhattan, 9/11 families gather at zuccotti park adjacent to ground zero. throughout the morning, it as has now become tradition, the names of victims will be read and four moments of sigh hence will mark the times each plane hit and each tower fell. vice president joe biden is attending the ceremony along with city and state leaders and first responders. at the pentagon, president obama delivers remarks and participates in a wreath laying ceremony. and in shanksville, pennsylvania, where united flight 93 crashed, first lady michelle obama along with former first lady laura bush attend a ceremony to honor the passengers who fought back. meanwhile plans to rebuild at ground zero are moving forward. the center piece, one world trade center, is expected to be completed by 2013. but with each construction step forward, there remains a connection to the past. steel beams pulled from the ground zero rubble were permanently insta